The present invention relates to a zoom interlocking mechanism for a binocular. More particularly, the invention relates to a zoom interlocking mechanism adapted to connect and drive zoom mechanisms of left and right telescopic optical systems via a belt.
In a known binocular having a zoom mechanism for variation of magnification, the left and right telescopic optical systems are integrated by the respective support arms connected to each other for rotation around the central shaft. The left and right zoom mechanisms are interconnected by a gear train including a central gear coaxially mounted on the central shaft. In a relatively large-sized binocular, the zoom operating member is pivotally or rotatably mounted on the central shaft, so that the left and right zoom mechanisms may be simultaneously driven by the central gear and the associated gear trains arranged at the left and right sides, relative to said central gear as said operating member is rotated. Such a binocular of prior art is disclosed in the U.S. Pat. No. 4,171,865 of the present applicant. In a relatively small-sized binocular, the zoom operating member is associated with one of the zoom mechanisms, so that rotation of said operating member causes both zoom mechanisms to be simultaneously driven by the gear train.
In the aforedescribed binoculars well known in the art, rotation of both support arms around the central shaft for interpupillary distance adjustment results in uneven rotation of the associated gears arranged at the left and right sides relative to the central gear. Consequently, the left and right zoom mechanisms are unevenly driven, so that the magnifications of both telescopic optical systems have different values.
Furthermore, a backlash inevitably occurs in the gear transmission mechanism. In a conventional, particularly compact, binocular, the backlash causes the magnification of the left and right telescopic optical systems to be disadvantageously uneven.
Also, the transmission driving mechanism using the gear is inconvenient, because its function is not smooth, mechanical engagement produces noise and a greater than negligible transmission loss occurs.
The aforedescribed drawbacks of the gear transmission mechanism have inevitably necessitated a construction too complicated to be practically realized. To overcome these drawbacks, it has been proposed to replace the gear transmission mechanism by the belt transmission mechanism.